Means for ringing over multiplex transmission channels



May 8, 1923 L. ESPENSCHIED MEANS FOR RINGING OVER MULTIPLEX TRANSMISSION CHANNELS Filed July 29, 1919 A TTORNEY Patented May 8, 1923.

TUNITED STATES PATENT OFFICE.

LLOYD nsrmrscnmn, or HOLLIS, NEW YO K. lessrenoa TO AMERICAN TELEPHONE -AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

MEANS FOR RINGING OVER MULTIPLEX TRANSMISSION CHANNELS.

Application filed July 29. 1919. Serial No. 814,674.

To all whom it may concem:

Be it known that I, LLOYD EsPENsoHInn, residing at Hollis, in the county of Queens and State of New York. have invented certain Improvements in Means for Ringing Over Multiplex Transmission Channels, of which the following is av specification.

This invention relates to transmission systems and more particularly to multiplex transmission systems employing carrier currents. U

Where multiplex transmission is attained by the use of carrier currents a plurality of carrier frequencies are transmitted over a common transmission line, the carrier frequencies being separated suiiiciently to prevent interference, and each frequency being assigned for use as a separate channel of communication so that signals, such, for instance, as telephonic variations, may be transmitted by impressing them upon the carrier frequencies. Several channels may -thus be superposed upon a common transmission line and each channel performs the functions of an ordinary telephone transmission line.

In ordinary telephone transmission it is customary to transmit over the line, in addition to the telephone currents, ringing currents or other signaling currents, for the purpose of signaling between operators in establishing connections. In order to obtain practical telephone service over each carrier communication channel. it is desirable that the channel be utilized for the transmission of such ringing or other signaling currents as well as forthe transmission of the ordinary telephone currents.

This invention therefore concerns means whereby ringing and other signals may be transmitted for each carrier channel.

' The invention also provides a transmission system in which is included an amplifier for amplifying certain frequencies to a greater degree than other frequencies.

A further provision of theinvention i a transmission system in which is included an amplifier adapted to amplify ringing current to a greater degree than voice currents.

Again the invention provides a transmission system including an amplifier having a feed back connection of' such character that a high degree of amplification for certain frequencies will result, while other frequencies'wlll be amplified to a lesser degree,

The invention likewise has reference to the provision of a transmission system having included therein a vacuum tube which normally acts to produce one desiredresult,

but which under other conditions, operates as a generator of oscillations.

A further feature of the invention is the provision in a transmission circuit of an amplifier, which, while normally serving as an amplifier only,will under certain conditions operate to produce oscillations.

' Still another part of the invention relates 1 to an amplifier between two line sections for the amplification ofcurrent transmitted from one line section to the other, which in response to currents transmitted from said last mentioned line section, will act as 'rier equipment is provided for separating the frequencies into their respective channels and for associating them with low frequency transmission lines. A ortion of the apparatus at one station on y is illus trated, it being understood that similar apparatus will be provided at'the other station. At the station illustrated in the drawing the main line ML is balanced by an artificial line MN and is associated through a balanced transformer arrangement 10, with a common transmittin circuit TL and a commonreceiving circuit ill), the arrangement being such that these two circuits are conjugate with respect to each other so that electrical variations arising in the one circuit will be without efl'ect upon the other.

The common transmitting and receivingnection including a filter TF, and the latter channel being inductively associated with the common receiving circuit RL, through a m tube amplifier of the connection including a filter RF The transmitting and receiving channels TL and RL are interconnected at their ends through a transformer arrangement 11 with the terminal line L the latter line beingIbalanced by an artificial line ornetwork so that the transmitting andreceivingchannels TL and BL, will be conjugate with respect to each other. The common transmitting and receiving circuits TL and BL may be similarly associated with one or more other low frequency terminal lines through transmittins, and receiving channels similar to TL and RL,, the manner in which additional channels are associated with the common circuits TL and RL, being indicated by the connections including the filters TF and RF,.

The transmitting channel TL includes. in addition to the filter-TF,', a similar filter TF These filters are preferably broad band filters of the general type i lustrated in U. S. patents issued to George A. Campbell, Nos. 1,227.113 and 1.227.114. dated May 22, 1917. These filters should be so designed as to transmit a band of frequencies equal in width to the band of frequencies employed in ordinary telephonic transmission, said band extending from the carrier frequency assigned to the channel to a limiting frequency either above or below said carrier frequency an amount equal to the width of the band.

In order to translate the low frequency signaling; currents transmitted over the line L, into high frequency currents for transmission over the main line ML, the transmitting channel TL is provided with a modulator M,. This modulator is preferably of the duplex vacuum tube type illustrated and described in the U. S. application of B. N. Kendall, Serial No. 125,349, filed October 13, 1916, or in the U. S. patent to John R. Carson, No. 1,343,307, issued June 15, 1920. The modulator M is supplied with carrier oscillations of the frequency assignedto the channel over a circuit 12, but as these oscillations are impressed on the common conductor of the balanced circuit normally no oscillations are transmitted through the modulator.

The transmitting channel TL. is also provided with an amplifier TA included in said circuit between the filters T1 and TR. This amplifier may be of any well known type, but as illustrated. is a duplex vacuum so-called push and pull type.

The receiving channel BL, includes, in addition to the filter RR. a filter RF These filters are likewise of the general type illustrated and described in the patents to Campbell above referred to, the filter RF being similar in structure and transmitting a band of frequencies similar to that transmitted by the filtersTF and TF The filter Rlfl', however, is a low frequency filter designed to transmit a range of frequencies extending from zero up to the upper limiting frequency employed in ordinary telephonic transmis- SIOII.

The receiving channel RL, also includes a demodulator or detector D,. This detector may be of any well-known type but is illus trated as being of the duplex vacuum .tube type, illustrated and described in the U. S. patent to John R. Carson, No. 1.343.308. issued June 15, 1920. As set forth in the said patent to John R. Carson this demodulator operates in accordance with the socalled homodyne method of receiving and is therefore supplied with oscillations of the same frequency as the correspondingniodulator. These oscillations are supplied over the circuit 13 to the common branch of the balanced input circuit of the demodulator so that normally no high frequency oscillations are transmitted through the demodulator.

,The receiving channel BL, is also provided with an amplifier RA, for the purpose of amplifying the detected low frequency currents. This amplifier may be of any Wellknown type. but asillustrated is a vacuum tube having its input circuit coupled with its output circuit through a connection inclu -ling a circuit 14 inductively coupled through a transformer 15 with a circuit including conductors 16, 17 and 18, conductors 16 and 18 being connected to one winding of a transformer 10 in the output circuit of the amplifier. Conductor 17 is normally connected in series with conductor 18 and includes acondenser 20, while the conductor 16 includes an inductance 21. A. condenser 22 is bridged across the prin'iary windings of the transformer 15. thereby forming a circuit resonant at a critical frequency.

In the amplification of telephonic currents which may be considered to extend over a range from about 300 cycles to about 2,000 cycles, the feed back connection above described is without substantial effect and the amplifier operates to amplify telephonic frequencies in the ordinary manner. desirable. however, that the detected ringing currents which will be impressed upon the amplifier as' hereinafter described, shall be amplified to a greater degree than the talking currents. These ringing currents should be of some frequency outside the telephone range described, as, for instance, 133 cycles. By means of the condenser 22. the circuit 14 is therefore tuned to resonate at 133 cycles. The primary of the feed back coil 15 is divided into two parts similar but reversed in respect to their subsequent circuits. The phase relations established by one of these circuits, that associated with a relay 23 is bridged across the receiving.

, ,ance to telep in general above 300 cycles. In order to.

condenser 20, is such as to cause reamplification but no singin of the feed back circuit, while that of t 0 other winding associated with condenser 35 is such as to cause singing. Each of the two primary circuits are tuned by means, respectively, .of condensers 20 and 35 to the frequency of the ringing v condition the feed back circuit is established through the reamplifying but non-singing secondary circuit asillustrated.

In order to control the transmission of ringing current of suitable frequency to the terminal line L, in'responsTe to ringing signals received, detected and amplified by theapparatus in the receiving channel RL,,

channel RL, beyond the filter RF, by means of a circuit tuned to 133 cycles through the agency of an inductance 24 and a condenser 25. This bridged circuit forms a' path of low impedance to ringing currents of 133 c cles, but offers a high impedhonic currents which may be insure that the maximum amount of ringing current shall flow through the bridge including the relay 23, a circuit including an inductance 26 and condenser 27 is serially inserted in one side of the channel RL, beyondthe bridge including the relay 23. The condenser 27 and the inductance 26 are so chosen as'to form a circuit which is antiresonant at 133 cycles, thereby preventing the bridge including the relay 23. The relay 23, while being unresponsive to currents of voice frequency, is readily responsive to ringing currents of 133 cycles and operates through relay 28 a relay 29, whereby the terminal line L, is disconnected from the channels TL, and RL, and ringing current from a local source of some suitable frequency, such as 16 cycles or 133 cycles is applied to said line. In order to prevent the unbalance of the two-way circuit including the channels TL, and RL, during this operation, the relay 29 also operates to connect an auxiliary network or resistance 30 across the terminals of the windings of the transformer 11 in order tobalance the artificial line'N,.

In order that the ringing signals incoming from the line L, may be transmitted over the line ML to a distant station through the transmitting channel TLp a relay 31 is bridged across the line L,, said relay being responsive to ringing current of any desirable frequency, as, for instance, 16 cycles or 133 cycles. This ringing responsive relay 31 upon being actuated operates through a'slow acting relay 32 to apply ringing current from a local source upon the input circuit of the modulator M,. While any local source of ringing current current. In the normal receivin the flow of current of this frequency beyond a may be utilized for this purpose, itis convenient to utilize the amplifier RA, as a source of ringing current. a

For this purpose the feed back'circuit'of the amplifier A, is so arranged that by the operation of relay 33 under the-control of relay 32, the conductor 18' is shiftedfrom connection with the conductor 17 and is serially connected to a conductor 34 includmg a condenser 35. This condenser is of such capacity as to resonate to 133 cycles the circuit which includes one primary winding of coil 15 and of the two primary windings is so connected that the feed back circuit causes the amplifier'RA, to oscillate at 133 cycles and to thereby generate ringing current. It is obmom that instead of the double primary winding illustrated, a single coil could be employed-and the relay arranged to switch coil 21. This one from a non-singing reamplifying connection sistance of the circuit.

In order that the-ringing current gener.

ated by the amplifierRA',"fmay"betransmitted to the modulator provided under the control of relay 32. said relay belng arranged to short circuit the line L, between the transformer 11 and the relay'31, thereby unbalancing the transformer connection between the transmitting channel TL, and the receiving channel RL, so that the channelsareno longer conjugate. The oscillations supplied by the amplifier RA, may therefore betransmitted'from the receiving channel RL, to the transmitting channel TL, and applied to the modulator M,. In order to prevent the os"illat ions thus transmitted from operating the relay 23 and in order to provide a transmission M, a relay 36 is rents, the relay 36 is arranged to' disconnect the bridge including the relay 23 and to short circuit the anti-resonant combination 26-27. 1

Further details of the apparatus will be clear from a description of the operation which is as follows:

Telephone currents incoming from the line L, are transmitted overthe outer back contacts of relay 29 and through the transformer 11 to the transmitting channel TL, without actuating the relay 31, the circuit of which is so designed as to offer a large impedance to' currents of telephonic frequency. The telephone currents upon being transmitted to the channel TL, are. iml

pressed upon the input circuit of the modulator M,. As already stated the circuit of the modulator M, is normally balanced so that carrier oscillations from the source 12 are not transmitted. The telephonic currents impressed upon -'the modulator, however, unbalance its circuit so that carrier responding to The telephone oscillations are transmitted by the modulator whose amplitude is directly proportional to the amplitude of the modulating voice wave. These modulated oscillations are passed through the filter TF amplified by the amplifier TA and then passed through the filter TF to the common transmitting circuit TL. Simultaneously modulated carrier currents of other frequencies from other channe s are impressed upon the circuit TL. The several modulated freguencies are transmitted through the transormer 10 and over the main line ML to the distant station.

Carrier currents having frequencies corthe several channels at the station of Fig. 1 and modulated at the distant station in accordance with telephone signals. after being transmitted over the line ML, pass into the common receiving circuit RL, from which the different carrier frequencies are selected into the proper receiving channels through the agency of filters such as RF RF etc. The modulated carrier oscillations passed through the filter RF are impressed upon the input circuit of the demodulator D where they react with unmodulated oscillations from the source 13 to produce in the output circuit of the demodulator low frequency telephonic currents corresponding to the telephone currents, in accordance with which the high frequency oscillations were modulated at the distant station. The low frequency telephone currents thus supplied are impressed upon the amplifier RA and are transmitted through the amplifier without substantially affecting the feed back circuit, which, as already stated, is so arranged as to cause the amplifier to reamplify oscillations having a frequency of 133 cycles which is below the lower limit of telephone currents. The telephone currents are therefore amplified by the amplifier RA, in the normal manner and are transmitted through the transformer 19, passing through the low frequency filter RF, to the midpoints of the transformer 11. The bridges including the relay 23 and the anti-resonant combination 26-27- do not materially decrease the transmission of the channel RL,, since they are designed to be affected with regard t'o currents in the neighborhood of 133 cycles only. currents upon arriving at the midpoints of the windings of the transformer 11 divide, part of the energy flowing to the artificial line N and part of the energy flowing over the back contacts of the relay 29 to the line L Ringing current transmitted over the line L, from a distant terminal station passes over the back contacts of the relay 29 and through the windin s of the ringing responsive relay 31. Con ensers 37 and 38 having a high impedance to ringing currents, but

readily permitting the passage of telephone currents, may be inserted between the relay 31 and the transformer 11 to insure that the greater proportion of the energy of the ringing current transmitted from the line 1L shall be impressed upon the relay 31.: Relay 31, in response to the ringing current opens a circuit of the slow acting relay 32 which completes circuits energizing. relays 33 and 36. Relay 33 upon being energized, at its left-hand contact disconnects ground from the normally opened circuit of the relay 29 to prevent any possibility of this relay being actuated to connect ringing current from a local source to the line L,., At its front left-hand contact relay 33' connects ground directly to the grid of the amplifier RA through the primary winding of the transformer 15, thereby short circuiting the potentiometer 39. At its right-hand front contact relay 36 disconnects conductor 18 from conductor 17 and connects it to conductor 34 which includes the condenser 35 so that the feed back circuit is so adjusted that the amplifier RA, oscillates at 133 cycles to generate ringing current. A distinct advantage arises from the short circuiting of the potentiometer 39 in the manner just described, due to the fact that the setting of the potentiometer is varied from time to time, under practical operating conditions, to vary the amplification of the amplifier RA is accordance with the transmission conditions of the circuit, and by short-circuiting the potentiometer, the amplifier when functioning as an oscillator will always be enabled to generate oscillations of the same amplitude.

The relay 36 upon being energized, at its right-hand front contact opens thebridge including the relay 23, thereby preventing said relay from being actuated by the 133 cycle oscillations supplied by the amplifier RA and at the same time it short circuits the anti-resonant combination 26-27, which, if it remained in the circuit would substantially prevent the transmission of the oscillations to the transformer 11. At its lefthand front contact relay 36 connects a short circuit across the left-hand terminals of the line windings of the transformer 11, thereby unbalancing the circuit so that transmission may take place from the receiving channel RL,, through the transformer 11 to the transmitting channel TL The 133 cycle oscillations are nowtransmitted from the amplifier RA through the filter RF, and

through the transformer 11 to the input circuit of the modulator M The 133 cycle oscillations thus transmitted operate to modulate the carrier frequency through the agency of the modulator M in the same manner as described in connection with telephone currents. High frequency oscillations while normally functioning to produce one ,10 and over the main line ML to the distant station. 7

In case it is desired to ring over the line -L, from the distant station the carrier apparatus at that station will be operated in a manner similar to that just described, so that carrier oscillations modulated in accordance with 133 cycle ringing current will be transmitted over the main line ML and into the common receiving circuit RL. The

4 carrier oscillations are. then selectively transmitted through the filter RF to the input circuit of the demodulator 1),. These modulated oscillations react in the demodulator D with unmodulated oscillations from the' circuit 13'to producevin the output circuit of the demodulator 133 cycle ringing currents, which are then impressed upon the amplifier HA This amplifier having its feed back circuit in its normal condition acts as a reamplifier at a frequency of 133 cycles and consequently the ringing currents .are amplified to a much greater degree than in the case of telephone currents. The highly amplified ringing currents are then passed through the filter RF, and flow through the bridge, including the relay 23 to operate said relay, the anti-resonant combination 2627 at the same time functioning to prevent any substantial amount of the ringing energy from being transmitted beyond the relay 23. Relay 23 upon being energized opens the circuit of the slow acting relay 28, thereby completing the circuit of relay 29, which at its outer front contacts disconnects the line L from the transformer 11 and a plies a local source of ringing current to sa d line. At its inner front contacts relay 29 at the same time substitutes an auxiliary line 30 for the line L so that the balance of the L is maintained.

It will be seen that by 'means of the arrangement above described a simple and yet efficient circuit has been provided whereby ringing signals may be transmitted over the same channel of a multiplex system as is used for telephonic transmission. It will also be seen that in accordance with this inventiona vacuum tube is provided, which,

transmitting and receiving channels TL and result, may be, under certaincircumstances, caused to function as a generator of ringing current, and, while in the system as herein disclosed, it has seemed most convenient to employ\the vacuum tube which normally functions as an amplifier for this purpose, any other vacuum tube in the system'might name to this equall well be used for the same purpose. It wil likewise be obvious that while the invention has been illustrated as embodied in certain apparatus which has been found to be desirable from a practical standpoint, the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the inven-' tion as defined in the following claims.

What is claimed is: I

1. In a signaling system, a source of telephone currents, a source of currents of frequencies WitllOIlt. the telephone range, a transmission circuit for transmitting from one source frequencies lying within the telephonic range, and for transmitting from the other source frequencies lying without said range, an amplifier in said circuit for amplifying all frequencies transmitted over said circuit, and means associated with said am-. plifier to give said amplifier a characteristic such that it will amplify certain frequencies Without the telephone range to a greater degree than frequencies within said range.

2. In a signaling system, a source of telephone current, a source of current of fretransmission circuit for transmitting from one source frequencies lying within the telephonic range, and for transmitting from the other source frequencies lying without said range, a device in said circuit for amplifying all frequencies transmitted over said circuit, a feed back coupling between the input and output circuits of said amplifier, said feed-back coupling being so adjusted that the amplification of said amplifier is augmented for certain frequencies lying without the telephone range.

3. In a signaling system, a source of telephone current, a source of signaling current, a transmission circuit for transmittin; telephonic frequencies and signaling frequencies from said sources, a device for amplifying both telephonic and signaling frequencies, and means for rendering the naling frequencies.

4. n a signaling system, a source of telephone current, a source of ringing current, a transmission circuit for transmitting telehonic frequencies and ringing frequencies rom said sources, a device for amplifying both telephonic and ringing frequencies, a feed back coupling between the input, and output circuits of said device so arranged that the amplification of the device will be greater for ringing frequencies.

In testimony specification this 28th day of July 1919.

- LLOYD ESPENSCHIED.

whereof, I have signed mv 

